The present invention relates to the field of computer driven plotters, particularly, scanning ink jet plotters in which a carriage having one or several ink jet devices thereon is supported above the paper or other medium on which plotting is to take place and moves transversely to the path of movement of the paper or other medium.
To obtain high resolution from an ink jet plotter, it is necessary to maintain a substantially constant vertical spacing between the ink jets and the drafting surface. To avoid smearing the ink, the means for supporting the carriage should not contact the plotted surface and contact of the carriage wIth the paper or other medium on which plotting takes place should be minimized. The prior art achieves this by slidably supporting the carriage on a support rod which is arranged transversely to the direction of movement of the paper. A single follower wheel, spring biased into engagement with a transversely extending guide surface disposed above the paper or other print medium prevents the carriage from pivoting about the slider rod on which it is mounted. The device maintains a substantially constant spacing of the printer head above the platen but does not automatically compensate for different paper widths or thicknesses since the single follower wheel does not ride on the paper. See, for example, U.S. Pat. No. 4,755,836 issued July 12, 1988 to the assignee of the present invention.
Slight vertical bowing or waves in the paper as it passes through the plotter and/or vertical bouncing of the carriage as it moves transversely of the paper on the support rods necessarily results in slight variation in the vertical spacing between the plotting ink jets and the paper surface with resulting unevenness of plotting quality. It is accordingly the object of the present invention to provide a means of maintaining a more constant spacing between the ink jets and the paper surface so as to improve the resolution of the plotted lines.